Our patients had combinations of previously reported risk factors, further increasing the likelihood of DVT, as follows: Case 1: FV Leiden homozygous mutation, chronic GVHD, and steroid use; Case 2: Protein S deficiency, chronic GVHD, and steroid use; Case 3: low protein C activity, elevated fibrinogen, and catheter use. The gene discussed is PROS1; the disease is deep vein thrombosis.